The present invention relates to devices and methods for shaping tooth filling material, such as composite resin, which has been placed in a tooth cavity preparation.
In dentistry, teeth which are subject to decay are typically drilled or otherwise prepared by removing the decayed tooth material. This leaves an aperture, slot or other void in the tooth which needs to be filled with composite resin or other filling material. When dentists fill class 2 cavity preparations, they typically insert a temporary substrate adjacent to the cavity preparation to contain and control the flow of filling material. The temporary substrate that dentists have traditionally used is an elongated band called a matrix band. The bands are typically placed in some type of a retaining device and then tightened around the prepared tooth by rotating a portion of the retaining device with the tightening being accomplished shortly before the filling process is begun. One example of a matrix band is found in U.S. Pat. No. 5,380,198 to Suhonen. This particular band has at least one window covered by a transparent strip of plastic such as cellulose acetate. The plastic strip rests against the dental filling material which may be cured using light. This patent also mentions retaining the matrix band in position with the aid of a matrix tightener such as used in a Tofflemire system.
One problem with conventional matrix band retaining devices is they are tightened by mechanical mechanisms which apply the force at a point midway between the gingival and occlusal border of the band. For example, such deviceds typically pinch the two ends of the band at a point midway between the gingival and occlusal border of the band and draw them through a slot (as in the Tofflemire matrix retainer) or wind the two ends around a rotating shaft (as in the Automatrix and other so-called spool retainers). Matrix bands are designed with a shape such that when they are placed in one of these retainers and tightened around a tooth with an average shape and taper, they will fit the tooth well. However when they are tightened around a tooth with a shape that tapers more than average, the bands do not fit the gingival margin well. Since adaptation of the matrix band at its gingival border is important to the success of the restoration, dentists often force wedges in between the teeth as close as possible to the gingiva in order to ensure good adaptation of the matrix band at the gingival border of the filling. Such wedge placement is time consuming and ineffective in enhancing adaptation on the buccal or lingual aspects of the interproximal area where there are no opposing surfaces to wedge against.
Another problem with conventional matrix band retainers is that, when they are used to tighten matrix bands around teeth, the force exerted is not resilient and is therefore difficult to control. The dentist typically applies force by turning a shaft until the shaft stops turning because the inner surface of the matrix band becomes tight against the outer circumference of the tooth at some point, preventing any further tightening. The dentist then simply stops turning the shaft and performs the filling, relying on the friction in the mechanism to prevent the shaft from turning slightly back and releasing the tension of the matrix band around the tooth. Some turning back of the mechanism may occur after the tightening has ceased.
Since most of the composite resins used to fill teeth today are light cured resins, clear plastic bands offer significant advantages over metal matrix bands. Composite resin can be observed by a dentist through the clear plastic band to ensure that there are no unfilled voids before curing. In addition, the composite resin may then be cured by shining light through the clear plastic band to ensure a better depth of cure. However, clear plastic matrix bands which are known to the inventors have been composed of strips of mylar (polyester) which is at least 0.0015 inch thick or plastic materials such as mentioned in U.S. Pat. No. 5,380,198. The materials in U.S. Pat. No. 5,380,198 are also understood to be relatively thick. This patent equates in one example, the thickness of the plastic to the thickness of a steel band included in the device of e.g., 0.05 mm thickness.
Therefore, there is a need for an improved apparatus and method for shaping tooth filling material. The present invention does not require the solution of all of the problems of the prior art. Instead, the invention is directed toward new and unobvious features and methods set forth in this disclosure both alone and in combination with one another and as set forth in the claims below.
In accordance with one embodiment, it is desirable for a tooth filling material shaping apparatus to be thin, have a light transmissive section, and be flexible enough so that it will closely follow the natural tooth contours when tightened around a tooth. It is also desirable in accordance with this embodiment to utilize a tightening device which holds the band tight around the tooth by means of light elastic forces.
In accordance with another aspect of an embodiment, a sheet of very thin polymer material is attached to a frame which defines at least one frame opening. The sheet may be a polymer film. Preferably the thickness of the sheet material positioned between the proximal or adjacent most surfaces of two adjacent teeth during filling of one of the teeth is no more than 0.0006 inch and preferably from about 0.0003 inch to 0.0006 inch. A light transmissive material, such as clear polyethylene may be used. The frame, which may be coupled to the sheet in any suitable manner, such as using adhesive or heat sealing, holds the plastic sheet taut in the frame opening and is flexible enough so that it can be easily bent or wrapped around a tooth to be filled. When positioned and tightened around the tooth, the frame is preferably flexible enough to closely follow the natural unprepared contours of the tooth being filled. A mechanism may be included for tightening the frame with the preferred approach involving the application of a tensioning force to at least the gingival portion of the frame.
The frame may contain an area which is easily severed, such as by breaking or by detaching detachably coupled frame elements so that the frame may easily be removed after a filling is complete without requiring the gingival portion of the frame to be pushed upwardly between contacting proximal teeth surfaces during the removal process. For example, the frame may be formed by a wire, which may be multi-stranded, with at least one frame opening being defined by looping the wire with first and second ends of the wire projecting outwardly from the loop. These ends of the wire may be positioned adjacent to one another and detachably secured together, for example by inserting the wires through a sleeve. This sleeve may be heat shrunk to more securely hold the wires together. Following completion of the filling, the ends of the wires may be removed from the sleeve and separated. The portion of the wire extending along the gingiva between adjacent teeth may then be pulled laterally until it emerges from between the teeth to thereby facilitate removal of the apparatus from a patient""s mouth. The frame may alternatively be cut or otherwise severed or broken to permit removal of the frame.
In accordance with an aspect of an embodiment, the frame may contain a mechanism which permits the dentist to fasten it to or hold it in position relative to a tooth being filled. Also, the frame is flexible such that the filling material shaping apparatus may be positioned and held in a wide variety of spatial relationships relative to the tooth to assist a dentist in achieving a desired contour when completing the filling. This increases the versatility of use of the device. As one specific example, the frame may include a mechanism which allows a dentist to tighten the gingival border of the frame around the tooth so as to enhance the close adaptation of the gingival margins of the completed filling so that the filling at such margins blends in smoothly with the remaining unprepared natural contours of the tooth. Close adaptation of the filling at the gingival margins is especially important because an overhang or an over-contoured area at the gingival margin may leave gingival tissues without sufficient functional stimuli to keep them healthy and may impair the ability of the patient to floss. The tightening mechanism may have some elasticity. Although desirable to tighten the apparatus by a tensioning force applied along the gingival border, and this may be the only location at which the tightening force is applied, it is also possible to tighten the apparatus by applying a biasing force at other locations such as the occlusal border.
The frame may also carry a section of sheet material which may be rolled, folded onto or otherwise positioned against the filling material on the biting surface of the tooth. This section may be unsupported and may comprise an occlusal extension section which can be positioned out of the dentist""s way until the filling material has been placed. Following placing of the filling material, including on the occlusal or biting surface of the tooth, the occlusal extension may be positioned onto the occlusal surface over the filling material. The patient may then bite down on the occlusal extension to directly mold a new restored bite surface.
Additional features of embodiments of the present invention are set forth in the detailed description below and shown in the drawings. The invention includes novel and unobvious elements, acts, features and methods described herein both individually and collectively and is not limited to any specific exemplary embodiments or approaches.